Process for deoxidizing copper



Patented Apr. 22. 1930 ,NITED STATES v PATENT CYRIL S. SMITH, OF CAMBRIDGE, MASSACHUSETTS, ASSIGNOB OF ONE-HALF TO CABLE R. HAYWARD, F QUINCY, MASSACHUSETTS PROCESS FOR .DEOXIDIZING CO?PER No Drawing.

This invention relates to a method for the treatment of copper for the purpose of improving its chemical purity and physical homogeneity and thereby raising the conductivity and ductility of the same.

' It is well known and generally acknowledged in the art that the presence in copper of an appreciable proportion of oxygen unfavorably affects the mechanical, electrical and chemical properties of the metal. It is therefore regarded as essential to remove most of the oxygen by appropriate reducing operations. This is commonly effected, with copper which has been previously oxygenlsated for the purpose of slagging ofi other impurities, by the operation known as poling. This consists in covering the charge of copper with charcoal or coke, insertingthe ends of green birch logs, or poles, into the 2e molten mass and leaving them there for a considerable period of time. In the course of this treatment, the liquid metal is actively agitated by the evolution of distillation products from the wood and the oxygen associated with the metal is rapidly removed. The oxygen content is customarily reduced in this manner to .03 to 05% and the resulting metal product is then used in known ways for the various purposes to which it is adapted.

It has heretofore been observed that copper as thus obtained and associated with greater or less amount of oxygen, is made exceedingly brittle if treated at elevated temperature with areducing gas such as hydrogen. Moreover, if this action is carried to any appreciable extent the metal becomes entirely useless for many purposes.

This embrittling effect has been attributed i by previous observers to various possiblecauses. such as the formation of reduced compounds of copper with the reagent substance 1 employed, such as a hydried for example. It has also been regarded as due to the formation of intergranular cracks by the creais formed by the combination of the hydrogen and the oxygen associated with the metal.

In any event, whatever may befthe true exlanation of the mechanism involved, copper which has thus been gassed is generally tion and explosive expansion of steam which Application filed July 8, 1926. Serial No. 121,270.

considered as ruined for all practical purposes and as requirlng a complete re-fusion en masse before it can be reworked. Hence it may be and is regarded as waste material, its former value having been entirely lost and no other procedure being hitherto availablefor its conversion to a desirable constitution or structure for subsequent working or for use per se.

It is therefore an object of this invention to provide a mode of treatment whereby oxygen may be removed from solid copper without re-fusion, and a product obtained which in general possesses an electrical conductivity and ductility superior to commercial grades of copper now available. It is a further object of the invention to impart substantial permanency to the finished metal even when subjected to reducing gases at elevated tem-- peratures. Other objects of the invention will be manifest from the following disclosure.

the copper, and thereafter consolidating the thus reduced copper mass to a state ofphysical continuity without undergoing any intervening oxidation.

In the research leading to and constituting a part of this invention it has been found a that copper which has been previously annealed, rolled, or otherwise Worked is not so susceptible to the ready penetration of reducing gases as is copper in its cast condition. It has further been established that, if ingots of cast copper, containing oxygen, are heated in'an atmosphere of a reducing gas, such as hydrogen, the gas penetrates the copper to a depth which depends upon: (I) the temperature of treatment; (II) the proportion of oxygen present therein; and (III) the duration of the treatment.

The efifect of temperature of treatment on the depth of penetration of the reducing gas I Briefly, and as summarized in one aspect into cast copper depends upon the initial amount of the oxygen in the metal. With low oxygen copper (that is up to 05%) the depth of penetration of the gas in any given time increases with rise of temperature. With copper containing larger amounts of oxygen (i. e., above .07 a muchgreater rate or depth of penetration by reducing gases is obtained. This increased rate or depth ofpenetration by reducing gases (with the more oxygenated coppers). is obtained the invention includes a preliminary reduction of the copper in its molten state by the usual methods,but preferably stopplng short of the degree of reduction usually effected or otherwise controlling the same thereby to reachthe oxygen content desired, casting the copper into convenient form for subsequent handling and subjecting the castings so produced to the reducing gas at a temperature favorable to gas penetration for the required period of time. The castings are then rolled, swaged, or otherwise consolidated out of contact with air or under any non-oxidizing conditions and preferably at higher than the usual temperatures for mechanical working.

The castings used may be in the form of cakes or wire bars of refined copper as commercially produced, and rolled or otherwise reviously worked copper may be employed.

ut, as noted above, it'is preferable to use it in the condition of castings or cast copper with high oxygen content, which is highly favorable to the reducing treatment in the solid state.

For purposes of illustration, a specific instance of the adaptation of the invention will be described, as carried out with castings of copper obtained by reducing purified copper by any commercial method to an oxygencontent of'approximately 12% to 15%. This may be accomplished by discontinuing the reducing operation considerably short of that usually employed where the ultimate product contains in the .vicinity of .05% oxygen or less, and pouring the molten metal into suitable molds. The castings thus obtained, in the form of a rectangular cake or bar or cylindrical rod for example,are fed into one end of a double-ended muffle type. of furnace in which an atmosphere of reduc- 1 ing gas, for example hydrogen, is mantained. The quantity of gas must be suificient to eflect complete reduction of the oxygen content of the metal, and to surround all portions of the charge under treatment. It is also to provide the required period of treatment so within the furnace chamber, two hours ordinarily being found sufficient with copper rods of approximately one inch to an inch and a quarter in thickness.

preferably maintained at an. approximate temperature of 810 C., (as by electric resistance units and thermostatic control means such as are commonly employed for such purposes) but adjacent to the exit end it is permitted to cool or is positively cooled sufficiently to bring the castings back to substantially atmospheric temperatures beforeleaving the furnace. The entrance and exit openings of the furnace are kept closed so far as is possible to prevent the introduction of air. This may be accomplished by refractory plates and also by maintaining the atmosphere of reducing gas at a positive pressure throughout the operations, as

already mentioned above. 1

l Vhen thus cooled before removing from thetreating chamber, the castingsmay be brought .into contact with the air without detrimental effect. But before again heating, preparatory to the second stage of treatment, if -this is to be carried out; in an oxidizing atmosphere they'may be rotected as by covering with copper foil. It is preferably, however, that oxidizing atmosphere, and to this end, a nonoxidizing gaseous atmosphere is maintained and the castings heated to a temperature suitable for rolling or other operationfor consolidating the same. upon the casting while surrounded by the non-reducing furnace atmosphere or immediately after removal therefrom. At this stage it is desirable that the temperature of the casting be somewhat above that. ordinarily employed,-e. g.,- for rolling, in the vicinity of 950 C.,and that the mechanical operation shall be sufficiently violent effectively to compact and profoundly consolidate the metal throughout its cross section. Other 125 similar operations might be substituted with like or corresponding effect, such as swagas the preliminary stage is conducted under penetra- 75 The temperature in the heating zone of the furnace is ss it be conducted in a non- This is carried out ing, forging, drawing and the like, so long operation has been accomplished the consolidated metal may thereafter be wlthdrawn directly into the air without serious efiz'ect event though it is still at a high temperature and whether or not aprotecting sheath of copper foil has been used thereon. Moreover, subsequent operations and manipulation of the metal may be carried out upon 1 paratus the metal may be carried directly from the initial reduction of the crude metal (after solidification) to the gassing treatment, then to the super heating and the first mechanical operation, in a reducing or nonoxidizing atmosphere, in a continuous succession of steps without intermediate cooling. Such an uninterrupted sequence of steps probably will be preferable in commercial operations although the provision of a supply of crude unworked ingots as above described may also be advantageous in many cases. 1

It will be obvious that numerous arrangements of apparatus maybe designed and constructed to accomplish the results above set forth-and described and that various combinations of conditions of treatment may be resorted to depending upon the characteristics ofthe raw material employed and the properties desired to be obtained in the resulting product. It is, however, to beunderstood that such variations and. adaptations are comprehended by the above disclosure and included within the scope of the following claims.

I claim:

1. A method for the treatment of copper containing oxygen, comprising reducing the same chemically at a temperature below the melting point, and consolidating the reduced metal to a condition of physical homogeneity.

2. A method for the treatment of copper containing oxygen, comprising subjecting the same to the action of a reducing gas at an elevated temperature, not exceeding the melting point, and consolidating the reduced copper to a condition of continuous homogeneity.

3. A method for the treatment of copper containing oxygen, comprising subjecting the same to the action of a reducing gas at a temperature within. a range including that of maximum penetrability of the metal .and consolidating the reduced metal to a condition of physical homogeneity.

4. A method for the treatment of copper containing oxygen, comprising subjecting the same to the action of a reducing gas at a temperature not exceeding the melting point and ducing gas, and thereupon consolidating the for a period of time to effect the desired degree of penetration of the metal by the rereduced metal to a condition of physical homogeneity.

5. A. method for the treatment of copper containing oxygen, comprising subj ecting the same to the action of a reducing gas at a tem= perature not exceeding the melting point, cooling in a non-oxidizing atmosphere, and

thereafter re-heating under non-oxidizing condition and consolidating the reduced metal to a condition of physical homogeneity.

6. A method for the treatment of copper containing oxygen, comprising subjecting the same to the action of a reducing gas at an elevated temperature not exceeding the melting point and consolidating the reduced met al to a condition of continuous homogeneity by hot working at a temperature above that usually employed.

7. A method for the treatment of copper containing oxygen, comprising reducing the same to a predetermined oxygen content, subjecting the same in the solid state to the action of a reducing gas at an elevated temperature not exceeding the melting point and consolidating the reduced metal to a condition of physical homogeneity.

8. A'method for the treatment of copper containing oxygen, comprising reducingthe same to. a predetermined oxygen content, subjecting the same in the solid state to the action of a reducing gas at an elevated temperature within the temperature range of maximum penetrability, and consolidating the reduced metal to a condition of physical homogeneity.

9. A method for the treatment of cast copper containing oxygen, comprising reducing the same to an oxygen content between .07 and 35%, subjectingthe same in the solid state to hydrogen at a temperature between 750 and 850 C. for the period required to produce the desired degree of penetration, and consolidating the same to the condition of physical homogeneity by subjecting it to hot working.

10. A method for the treatment of cast copper containing an appreciable amount of oxygen, comprising subjecting the same to the action of hydrogen at a temperature within the range of maximum penetration and consolidating the reduced metal to a condition of physical homogeneity.

11. A method for the treatment of cast copper containing an appreciable amount of oxygen, comprising subjecting the same to the action of hydrogen at an elevated temperature not exceeding the melting point and consolidating the reducedmetal to a condition of physical homogeneity.

Signed by me at Boston, Massachusetts this first day of July,.1926.

" CYRIL S. SMITH. 

